The present invention relates to a picture viewer for viewing sequentially pictures in a stack. The picture viewer includes an exchange mechanism which cylically exchanges the picture in the stack that is presented for viewing at a viewing window.
Picture viewers for sequentially viewing a stack of pictures are described in U.S. Pat. No. 4,259,802 (the '802 patent). Picture viewers of the type described in the '802 patent are discussed in some detail in my U.S. patent application Ser. No. 560,384, filed concurrently herewith, the disclosure of which is incorporated herein by reference.
Briefly, the picture viewer of the '802 patent comprises a housing with a viewing window and a slider or drawer which may be reciprocated into and out of the housing parallel to the plane of the viewing window. The housing has a spring bias system adapted to urge a stack of pictures against the window when the slider is positioned in the housing.
The slider is provided with a separator bar adapted to force all but the top or bottom picture in the stack of pictures out of the housing when the slider is moved out of the housing. A retentive coating on the spring bias system retains the uppermost or lowermost picture of the stack in the housing upon the outward stroke of the slider thus separating that picture from the rest of the stack of pictures. On the return stroke of the slider, the separated picture is returned to the opposite end of the stack from which it was removed.
On the outward and return strokes of the slider, the separator bar passes first over and then under the separated picture, or vice versa, depending on whether the top or bottom picture in the stack is removed from the stack on the outward stroke. Appropriate spaces are, therefore, provided above and below the separator bar to accommodate the separated picture on the outward and return strokes of the slider.
By combining the spring bias system and the retentive coating into one element in the housing, as described above, certain advantages with respect to the ease of manufacture of the picture viewer may be achieved. However, the viewer described above also has certain drawbacks. In particular, upon each outward stroke of the slider, the separator bar must engage and suppress the spring bias system. The forces necessary for such suppression vary considerably over the length of the outward stroke. As a result, the user has the feeling of "jamming" at certain positions in that stroke. Thus, a design in which a relatively uniform force is required to move the slider out of the housing would be highly desirable.